Apply fixes from StyleCI

[mechelon]

This pull request applies code style fixes from an analysis carried out by StyleCI.

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[what-the-diff]

• Removed the use of Page class in NotionQueryBuilder.php
• Added a missing dot to concatenate strings in pluck() method and queryToNotion() method
• Fixed typo error by adding a missing space between two variables $this->modelClass::$preCacheKey.$this->modelClass::$databaseId.$postCacheKey;